The present invention relates to a data erasure apparatus, a data erasure method and a method for writing servo patterns on a recording disk.
A typical hard disk drive (HDD) comprises a magnetic disk, a spindle motor to drive the magnetic disk to rotate, a magnetic head to write/read data to/from the magnetic disk, and others. The HDD has an enclosure case which accommodates the components. The enclosure case is generally made of a boxy base having an opening and a top cover plate covering the opening of the base.
Assembling of the disk device is completed when the opening of the base is covered by the top cover after the components are mounted in the base. After the assembly is completed, servo patterns are written on the magnetic disk. After the writing of servo patterns is completed, the HDD is put to various tests before shipment. If judged defective, the HDD is disassembled to collect and reuse non-defective components. To reuse the magnetic disk, however, it is necessary to erase the servo patterns written thereon since otherwise the servo patterns may interfere with new servo patterns to be written. Also if the written servo patterns themselves are judged not good, the servo patterns must be erased. Further, test data are written in pre-shipment test. If the disk device does not pass the test, it is also necessary to erase the test data.
As for erasing data from magnetic disks, International Patent Publication WO98/49674 discloses an apparatus capable of erasing data from magnetic disks in a condition where magnetic disks are mounted in an HDD. This apparatus comprises two upper permanent magnets which are adjacently positioned with opposite poles faced so as to attract each other, and two lower permanent magnets which are also adjacently positioned with opposite poles faced so as to attract each other. In addition, they are perpendicularly arranged such that like poles are faced with each other.
In a central area between the permanent magnets, a mainly horizontal magnetic field is formed. Today, horizontal magnetic recording is employed for magnetic disks. Accordingly, letting the horizontal magnetic field act on a magnetic disk erases the data stored on the magnetic disk. The strength of the magnetic field must be higher than the coercive force of the magnetic disk. While the magnetic disk is rotated in the magnetic field, the horizontal magnetic field acts over the whole surface of the magnetic disk to erase the data. By using the external field by the permanent magnets, the data on the magnetic disk can quickly be erased.